The present disclosure relates to a hydraulic control device for an automatic transmission mounted on an automobile, for example, and specifically relates to a hydraulic control device for a shift-by-wire-type automatic transmission that can switch travel ranges with a plurality of switching valves that are electrically controlled.
Conventionally, a shift-by-wire-type range switching device including two switching valves and two solenoid valves that can switch the respective switching valves has been known (see Japanese Patent Application Publication No. 2013-185656). In this range switching device, a combination of spool positions of the two switching valves allows switching among a forward range state, a reverse range state, and an N range state. Furthermore, in this range switching device, when one of the two solenoid valves fails, the N range state is formed by operation of the other of the solenoid valves. This enables the range switching device to prevent formation of an unintended shift speed for forward or reverse traveling when either one of the two solenoid valves fails.
Another shift-by-wire-type range switching device including two switching valves and two solenoid valves that can switch the respective switching valves has also been known (see FIG. 12 in Japanese Patent Application Publication No. 2008-128473). In this range switching device, a first switching valve switches between outputting input line pressure as a range pressure and blocking the input line pressure, and a second switching valve can switch the range pressure input from the first switching valve between forward range pressure and reverse range pressure to output the resulting range pressure. In this range switching device, the first switching valve is configured to be self-held with the output range pressure. This enables the range pressure output from the first switching valve to be maintained, thereby maintaining the traveling state even in the event of off failure of the solenoid valve for switching the first switching valve during traveling.